JPH0680527B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk. More specifically, it relates to a magnetic recording medium using a thermoplastic polyurethane resin having excellent properties as a binder component of a magnetic layer provided on a non-magnetic support.

(Prior Art) A magnetic tape, which is a general-purpose magnetic recording medium, has acicular magnetic particles with a long axis of 1 μm or less dispersed in a binder solution together with an appropriate additive (dispersant, lubricant, antistatic agent, etc.). It is manufactured by making a magnetic paint and applying it to a polyethylene terephthalate film.

Properties required for the binder of the magnetic recording medium include dispersibility of magnetic particles, filling property, orientation, magnetic layer durability, abrasion resistance, heat resistance, smoothness, adhesion to non-magnetic support, etc. The binder plays a very important role. Conventionally used binders are vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate / vinyl alcohol copolymers, vinyl chloride / vinylidene chloride copolymers,
Polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer, nitrocellulose, cellulose acetate butyrate, epoxy resin or acrylic resin are used.

Among these resins, polyurethane resin is superior in properties such as toughness and abrasion resistance to other resins due to intermolecular hydrogen bond by urethane bond, but has a major drawback that the dispersibility of magnetic particles is poor. is there. In order to improve the dispersibility, it has been found by the present inventors that it is effective to introduce a specific phosphorus compound or a metal salt thereof into a resin (Japanese Patent Application No. 58-128470 and Japanese Patent Application No. 128470). 59-1703
No. 7). However, in order to improve the S / N ratio of the magnetic recording medium,
Although the introduction of a specific phosphorus compound or a salt thereof is recognized to have an effect on the requirement of high packing of filling magnetic particles in the magnetic layer as much as possible, the requirement of highly dispersing finely divided magnetic particles, etc. The current situation is that we are not satisfied.

Further, the conventional adipate type or caprolactone type polyurethane resin alone is inferior in properties such as blocking resistance, heat resistance and running stability. Therefore, a mixed system of a polyurethane resin and nitrocellulose or a vinyl chloride / vinyl acetate copolymer is particularly used. However, in terms of characteristics such as durability, abrasion resistance and running stability, it is still insufficient in the fields requiring high performance such as video tapes, computer tapes and floppy disks.

As a method for improving the durability, abrasion resistance, running stability, etc. of the magnetic recording medium, a lubricant such as higher alcohol, long chain fatty acid or its ester compound, silicone oil, and fluorine-containing compound is used to It is known to reduce the friction coefficient, but in this case, the deterioration of running characteristics due to additive bleeding on the surface of the magnetic layer, clogging of the head, or the low molecular weight compound is a problem. There is a defect that the strength of the coating film decreases due to the inclusion in the layer.

In order to overcome these drawbacks of the method of adding a lubricant, attempts have been made to incorporate a lubricant component into the binder. For example, in JP-A-58-218034, a polyurethane resin containing a polydimethylsiloxane dicarbinol having a dimethylsiloxane bond, which is a constituent of general-purpose silicone oil, as a polyol component is described as a binder for a magnetic recording medium. ing. JP-A-58-2180 mentioned above
When a polyurethane resin containing a polyalkylenesiloxane dicarbinol as a polyol component described in JP-A No. 34-34 is used as a binder for a magnetic recording medium, as described in JP-A-58-218034, abrasion resistance is improved. Although it is excellent in durability and running stability, it has very poor adhesion to polyethylene terephthalate film, which is a general-purpose non-magnetic support, and poor dispersibility of magnetic particles, especially high filling of magnetic particles. However, it is not effective in improving the dispersibility of finely divided magnetic particles. In addition, the compatibility with other resins is extremely poor, and it is practically impossible to mix and use the other resins. Therefore, the properties required for the binder of the magnetic recording medium, such as heat resistance, cannot be obtained by using this resin alone. , The cold resistance, the appropriate stiffness, the adhesion to a non-magnetic support, etc. must be satisfied, but the polyurethane resin alone described in JP-A-58-218034 cannot satisfy the properties required for the binder. .

Introducing a polysiloxane bond into the polyurethane resin means that the polysiloxane bond having a hydroxyl group in the molecule is incompatible with a general-purpose polyurethane raw material such as adipate type polyester diol or polycaprolactone. This is difficult with the conventional manufacturing method. Even if it is obtained, the solution becomes insoluble or cloudy in a general-purpose organic solvent such as toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and ethyl acetate used in the production of magnetic recording media.

(Problems to be Solved by the Invention) In view of the above circumstances, the objects of the present invention are as follows.

To provide a magnetic recording medium having excellent dispersibility, filling property and orientation of magnetic particles.

We have found a polyurethane resin with a polysiloxane bond in the molecule, which has excellent adhesiveness to polyester film, compatibility with other resins, solubility in general-purpose organic solvents, etc., and abrasion resistance using this polyurethane resin as a binder component. Another object of the present invention is to provide a magnetic recording medium excellent in durability, running stability, adhesiveness with a polyester film and the like.

(Means for Solving Problems) In the present invention, one component of the raw material as a binder component is 2 in one molecule.
A polyurethane resin obtained by introducing a specific phosphorus compound or a metal salt thereof into a molecule, which is obtained by using a limited polysiloxane compound having one hydroxyl group is characterized.

That is, the present invention relates to a magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, and an organic diisocyanate (A) and a polyester having a molecular weight of 500 to 5,000 are used as components of the binder. A polyurethane resin having a molecular weight of 6,000 to 50,000, which is obtained by reacting a diol (B), a polysiloxane compound (C) represented by the following general formula (I), and optionally a chain extender (D) having a molecular weight of less than 500: At least one kind of the polyester diol (B) having a molecular weight of 500 to 5,000 is a polyester diol obtained by copolymerizing a phosphorus compound represented by the following general formulas (III) to (VIII) in the molecule. It is a magnetic recording medium.

General formula (I): (In the formula, R ₂ and R ₃ are an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, and R ₁ and R ₄ are represented by the general formula (II): R ₅ is a hydrogen atom or a methyl group, and R ₆ is an alkylene group having 2 to 10 carbon atoms. m is an integer of 0-5. Further, n is an integer of 5 to 50. ) General formula (III): General formula (IV): General formula (V): General formula (VI): General formula (VII): General formula (VIII): [In the formula, R ₇ is a trivalent hydrocarbon group having 3 to 10 carbon atoms, and R _{8 is}
Represents an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group or a phenyl group. R ₉ and R ₁₀ represent an alkylene group having 1 to 4 carbon atoms. X and Y are ester-forming functional groups, M
Represents an alkali metal atom, hydrogen or an alkyl group having 1 to 4 carbon atoms. The organic diisocyanate (A) used in the production of the polyurethane resin used in the present invention includes 2,4-
Tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-bif Enylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether,
1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,
Examples thereof include 3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, 4,4-diisocyanate dicyclohexane, 4,4-diisocyanate cyclohexylmethane, and isophorone diisocyanate.

The polyester diol (B) used in the production of the polyurethane resin used in the present invention has a molecular weight of 500 to
It is in the range of 5,000, and the raw material components are as follows except for a specific phosphorus compound.

Examples of the carboxylic acid component of the polyester diol include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, aromatic oxy acids such as p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid. Examples thereof include aliphatic dicarboxylic acids such as carboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Examples thereof include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and hydrogenated 2,6-naphthalenedicarboxylic acid.

As the glycol component of polyester diol,
Ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4- Trimethyl-1,3-pentanediol, cyclohexanedimethanol, bisphenol A ethylene oxide adduct and propylene oxide adduct,
There are ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.

Trifunctional components such as trimellitic anhydride, trimethylolpropane, and glycerin are used in a range that does not impair the performance, and it is desirable that the total dicarboxylic acid component or total glycol component is 7
You may use it in the range of mol% or less. Other polyester diols include lactone polyester diols obtained by ring-opening polymerization of lactones such as ε-caprolactone.

Particularly, 30% by weight or more of the polyester diol, 50 to 100 mol% of the dicarboxylic acid component is an aromatic dicarboxylic acid, and 50 to 100% by mole of the dicarboxylic acid component.
0 mol% contains aliphatic and / or alicyclic dicarboxylic acid, 25-100 mol% of the glycol component contains neopentyl glycol, 75-0 mol% contains C2-C10 aliphatic, alicyclic, aromatic ring When the polyester diol is composed of one or more glycols selected from glycols, the resulting polyurethane resin has excellent adhesiveness to polyethylene terephthalate, which is a general-purpose non-magnetic support, and also has good abrasion resistance. Therefore, it is preferable.

The phosphorus compound that characterizes the polyurethane resin used in the present invention is to be copolymerized in polyester diol and can be represented by the general formulas (III) to (VIII).
The following can be mentioned as specific examples.

As the one represented by the general formula (III), What is represented by the general formula (IV) is As the one represented by the general formula (V), What is represented by the general formula (VI) is What is represented by the general formula (VII) is As the one represented by the general formula (VIII), The polyester diol (B) having a molecular weight of 500 to 5,000 used for producing the polyurethane resin used in the present invention is obtained by copolymerizing the above-mentioned phosphorus compound with 0.1 to 20 mol% of all dicarboxylic acid components or all glycol components. At least one component. Phosphorus compound is 0.1 for all dicarboxylic acid components or all glycol components
If it is less than mol%, the dispersibility of magnetic particles is not improved, and
If it exceeds mol%, the compatibility is deteriorated when a polyester diol containing no phosphorus is used together, and a uniform resin cannot be obtained. Also, when used alone, the hygroscopicity is increased, the solution viscosity is increased, and the compatibility with other resins is deteriorated, which is not preferable. The phosphorus content based on the general formulas (III) to (VIII) is preferably 0.01 to 2% by weight in the polyurethane resin.

The polyester diol (B) has a molecular weight of 500 to 5,000. If the molecular weight is less than 500, the urethane group concentration will increase, and the flexibility and solvent solubility of the resin will decrease. On the other hand, if the molecular weight exceeds 5,000, the concentration of urethane groups decreases, and the toughness and abrasion resistance peculiar to polyurethane resins deteriorate.

The polysiloxane compound (C) used in the production of the polyurethane resin used in the present invention is represented by the general formula (I) having hydroxyl groups at both terminals of the molecule.

(R ₂ and R ₃ are an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, and R ₁ and R ₄ are represented by the general formula (II): R ₅ is a hydrogen atom or a methyl group, and R ₆ is an alkylene group having 2 to 10 carbon atoms. m is an integer of 0-5. Further, n is an integer of 5 to 50. ) In the general formula [I], some of R ₂ and R ₃ have 1 to 10 carbon atoms.
It may be an alkyl group of 6 or a phenyl group.

The following are examples of specific compounds.

Polysiloxane compound (C) represented by general formula (I)
Is used in the range of 0.01 to 20% by weight, preferably 0.5 to 10% by weight of the polyester diol component (B) having a molecular weight of 500 to 5,000. If the polysiloxane compound (C) is less than 0.01% by weight of the polyester diol component (B), there is no effect of using the polysiloxane compound (C).
If the content exceeds 10% by weight, the adhesion to polyethylene terephthalate film, which is a general-purpose non-magnetic support, decreases, the compatibility with other resins deteriorates, the solubility of the resulting polyurethane resin in general-purpose organic solvents decreases, etc. Cause

The chain extender (D) having a molecular weight of less than 500, which is optionally used in the present invention, has the effect of adjusting the urethane group or urea group concentration in the resin and imparting toughness peculiar to the polyurethane resin. Include ethylene glycol, 1,3-propylene glycol, 1,4-tetramethylene glycol, 1,6-hexanediol, cyclohexanedimethanol, xylylene glycol, diethylene glycol, triethylene glycol, and an ethylene oxide adduct of bisphenol A. Branching of linear glycol, propylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,2,4-trimethyl-1,3-pentanediol, propylene oxide adduct of bisphenol A, etc. Glycol, monoethanolamine, N-methylethanol Amino alcohols such as amines, ethylenediamine, hexamethylenediamine, isophoronediamine, diamine or water such as piperazine and the like.

As chain extenders other than the above, trifunctional components such as trimethylolpropane, diethanolamine, triethanolamine, and glycerin may be used within a range that does not impair the performance.

If the molecular weight of the chain extender (D) exceeds 500, the toughness peculiar to the polyurethane resin decreases, which is not preferable.

The chain extender (D) is preferably used in the range of 0 to 5 times the equivalent weight of the polyester diol (B) having a molecular weight of 500 to 5,000. If the amount exceeds 5 times the equivalent, the solubility in a general-purpose organic solvent may decrease depending on the type of chain extender.

When producing the polyurethane resin used in the present invention, the ratio of the isocyanate group to the hydroxyl group is in the range of 1 / 0.85-1.25, and this ratio determines the molecular weight of the polyurethane resin obtained. Under conditions where the isocyanate group is excessive with respect to the hydroxyl group, the resulting polyurethane resin is less than the isocyanate group, so that the storage stability is poor, and since the molecular weight of the polyurethane resin becomes too low when the hydroxyl group is too large, the preferred range is 1 / It is 1 to 1 / 1.15.

The molecular weight of the polyurethane resin is in the range of 6,000 to 50,000. If the molecular weight is less than 6,000, the mechanical strength of the polyurethane resin will decrease, and if it exceeds 50,000, the solution viscosity will be too high and handling will be difficult.

The polyaddition reaction of the polyurethane resin used in the present invention is a one-shot method in which all components are reacted at the same time, first, a long-chain diol is reacted under conditions of excess isocyanate, and the resulting isocyanate group-terminated prepolymer is added with a chain extender.
There is a prepolymer method for further polymerizing. The polyurethane resin used in the present invention can be manufactured by either one-shot method or prepolymer method. Examples of the reaction method include a method in which the raw materials are melted and a method in which they are dissolved in a solution.

Stannous octylate, dibutyltin dilaurate, triethylamine and the like may be used as the reaction catalyst.

Paratoluene sulfonic acid, butadiene sulfone, an inorganic acid, an oxy acid or the like may be used to prevent gelation during the urethanization reaction.

Further, an ultraviolet absorber, a hydrolysis inhibitor, and an antioxidant may be added before, during, or after the production of the polyurethane resin.

In the present invention, in addition to the polyurethane resin used in the present invention, other resin is added for the purpose of adjusting flexibility, improving cold resistance and heat resistance, and / or reacting with the polyurethane resin. It is desirable to mix compounds that crosslink. Other resins include vinyl chloride resin, polyester resin, cellulose resin, epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile-
Examples thereof include butadiene copolymer. On the other hand, as the compound that crosslinks with the polyurethane resin, there are polyisocyanate compounds, epoxy resins, melamine resins, urea resins and the like, and among these, polyisocyanate compounds are particularly desirable.

As the ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention, γ-Fe ₂ O ₃ , mixed crystal CrO _{2 of} γ-Fe ₂ O ₃ and Fe ₃ O ₄ ,
Examples thereof include cobalt-doped γ-Fe ₂ O ₃ or Fe ₃ O ₄ , parium ferrite, and ferromagnetic alloy powders such as Fe—C ₀ and Fe—C ₀ —Ni.

The magnetic recording medium of the present invention may optionally contain a plasticizer such as dibutyl phthalate, triphenyl phosphate, dioctyl sulfo-sodium succinate, t-butylphenol polyethylene ether, ethylnaphthalene.
Lubricants such as sodium sulfonate, dilauryl succinate, zinc stearate, soybean oil lecithin, silicone oil and various antistatic agents can also be added.

(Function) The polyurethane resin used in the present invention contains a specific polar compound having a high polarity and a non-polar polysiloxane compound in the molecule, and the introduction of the phosphorus compound improves the dispersibility of the magnetic particles. It is further increased by introducing a siloxane compound. Properties resulting from dispersibility, such as filling properties of magnetic particles, orientation, and smoothness of the magnetic layer are also improved. By limiting the proportion and type of the polysiloxane compound, not only the wear resistance, durability, and running stability of the magnetic layer are excellent, but also the adhesiveness with a polyester film, which is a general-purpose support for magnetic recording media, etc. Good compatibility with resin.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples. In the examples, "parts" means "parts by weight".

Each physical property was measured according to the following methods.

Fillability: Porosity (Rv) was calculated by the following formula.

Rv = 1-Ms / q · Mo (Ms: saturation magnetization of magnetic coating film per unit volume, Mo: saturation magnetization of only magnetic powder per unit volume,
q: The smaller the volume fraction and porosity of the magnetic powder in the magnetic coating film,
The filling rate is large and the S / N ratio can be improved and the recording density can be increased.) Gloss of magnetic layer: Measure 60 degree gloss.

Wear condition after 100 runs: Put a magnetic tape on the video deck and observe the wear condition of the magnetic layer after 100 runs.

Running stability: I put magnetic tape on the video deck and saw unevenness when running.

Adhesiveness with polyethylene terephthalate (PET) film: Cellotape was attached to the surface of the magnetic layer, and the degree of peeling between the magnetic layer and the PET film was observed when the cellotape was peeled off.

○ …… No peeling at all △ …… Almost half peeling × …… Full surface peeling Synthetic example of polyester diol 194 parts dimethyl terephthalate, 194 parts dimethyl isophthalate in an autoclave equipped with a thermometer and a stirrer,
Ethylene glycol 149 parts, neopentyl glycol 166
And 0.05 parts of tetrabutoxytitanate, 15 parts
The mixture was heated at 0 to 230 ° C for 120 minutes for transesterification, then 11 parts of sodium 2,3-dihydroxypropylphenylphosphonous acid (phosphorus compound) was charged, and the reaction was further conducted at 220 ° C for 1 hour.

Then, the reaction system is heated to 240 ° C in 30 minutes, the system pressure is gradually reduced, and 45 minutes later, the pressure is reduced to 1 to 3 mmHg, and further 3
The reaction was continued for 0 minutes. The obtained polyester diol had a molecular weight of 2,500, and composition analysis by NMR and phosphorus content measurement revealed that terephthalic acid / ethylene glycol isophthalate / neopentyl glycol / 2,3-dihydroxypropylphenyl sodium phosphonate = 50/50/55 / 43/2
(Molar ratio).

Similarly, polyester diols listed in Table 1 were obtained. Polyester diol is obtained by copolymerizing a phosphorus compound with 0.05 mol% and 25 mol% of all glycol components, and does not contain a phosphorus compound.

Polyurethane resin synthesis examples 1 to 14 In a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, 151 parts of toluene, 151 parts of methyl etorketone, 100 parts of the polyester diol, 5 parts of neopentyl glycol and gelation. P-toluenesulfonic acid as an inhibitor
0.01 parts, polysiloxane compound of molecular weight 1,000 (a)
(2) The above (2 parts) was charged, and after dissolution, 22 parts of 4,4'-diphenylmethane diisocyanate and 0.05 part of dibutyltin dilaurate were charged and reacted at 70 to 80 ° C for 10 hours.

The resulting polyurethane resin (A) solution has a solid content of 30
%, The solution viscosity was 50 poise (25 ° C.), and the molecular weight of the polyurethane resin (A) was 21,000.

In addition, the obtained polyurethane resin (A) solution was added to nitrified cotton (RS1 / 2 made by Daicel), vinyl chloride / vinyl acetate resin (VAG made by UCC)
The MEK / toluene (1/1) solution of (H) was mixed so that the solid content ratio was 1/1 and the solid content concentration was 20%, and the compatibility was measured.
After being uniformly mixed, when 5 hours was allowed to stand at room temperature, phase separation occurred, and when the uniform state was maintained, the compatibility was good (◯).

Similarly, the polyurethane resin (B) described in Table 2 ~
(N) was obtained. The results of resin properties and compatibility tests are
Shown in the table.

Comparative Synthesis Examples 1 to 7 of Polyurethane Resin
Polyester diol (molecular weight 2,000, phosphorus compound not copolymerized) was used instead of polyester diol] to obtain a polyurethane resin (O) ^* solution. The solid content concentration was 30%, the solution viscosity was 7 poise (25 ° C.), and the molecular weight of the polyurethane resin (O) ^* was 25,000.

Polyurethane resins (O) ^* to (Z) ^* were obtained from the raw materials shown in Table 2 by the method of Synthesis Example 1.

In Table 1, phosphorus compounds are shown below.

2,3-Dihydroxypropyl-sodium phenylphosphinate 2,3-dihydroxypropyl-phenylphosphinic acid 2,3-dihydroxypropyl-sodium phenylphosphinate 2,3-dihydroxypropyl-phenyl phenylphosphonate 2,3 -Sodium dihydroxypropyl-2-sodium oxyphenyl phosphinate bis (hydroxypropyl) sodium phosphinate sodium bis (hydroxypropyl) phosphonate sodium carboxyethyl-ethoxy ethoxy phosphonate In Tables 1 and 2, symbols and abbreviations. Indicates the following:

PBA: polybutylene adipate PCL: polycaprolactone MDI: 4,4'-diphenylmethane diisocyanate TDI: 2,4-tolylene diisocyanate IPDI: isophorone diisocyanate NPG: neopentyl glycol HD: 1,6-hexanediol DEG: diethylene glycol solvent (X ): Methyl ethyl ketone / toluene = 1/1 weight ratio Solvent (Y): Methyl acetate Solvent (Z): Methyl ethyl ketone Example 1 A composition having the following blending ratio was placed in a ball mill and dispersed for 48 hours, and then an isocyanate compound, Coronate 2030
5 parts (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent and further mixed for 1 hour to obtain a magnetic paint. This thickness
It was applied onto a 12 μm polyethylene terephthalate film while applying a magnetic field of 2,000 glass so that the thickness after drying was 5 μm. After standing at 50 ° C. for 2 days, it was slit into a 1/2 inch width to obtain a magnetic tape.

Polyurethane resin (A) solution 100 parts (solid content 30%, MEK / toluene = 1/1 solution) Cobalt-deposited γ-Fe ₂ O ₃ 120 parts Olive oil 1 part Cyclohexanone 50 parts Toluene 100 parts MEK 50 parts Obtained Table 3 shows the gloss of the magnetic layer of the magnetic tape, the filling degree of the magnetic particles, the abrasion state after 100 times of running, and the adhesive with the polyethylene terephthalate film.

Examples 2 to 19, Comparative Examples 1 to 12 Instead of the polyurethane resin (A) used in Example 1,
A magnetic tape was obtained in the same manner as in Example 1 except that the resins listed in Table 3 were used. The evaluation results of each are shown in Table 3-1 to 3.

The weight ratio of the binder to the magnetic particles is 1/4.

In Table 3-1 to 3 below, other resins blended in the polyurethane resin solution are as follows.

(Effects of the invention) As is clear from Tables 3-1 to 3 of Examples and Comparative Examples, a polyester diol (B) and a polysiloxane compound (C) obtained by copolymerizing a phosphorus compound were used within the scope of the present invention. The polymerized polyurethane resin is excellent not only in the dispersibility of magnetic particles but also in the filling property of magnetic particles.

A magnetic recording medium using the above polyurethane resin is excellent in squareness ratio, filling property of magnetic particles, abrasion resistance, running stability, and adhesiveness with a PET film.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support coated with a magnetic material in which a ferromagnetic powder is dispersed in a binder.
As a component of the binder, an organic diisocyanate (A),
Polyester diol (B) having a molecular weight of 500 to 5,000 and polysiloxane compound (C) represented by the following general formula (I)
Of the polyester diol (B) having a molecular weight of 6,000 to 50,000 and having a molecular weight of 500 to 5,000 obtained by reacting Phosphorus compound for all dicarboxylic acid components or all glycol components 0.1 to 20
A magnetic recording medium characterized by being a polyester diol copolymerized by mol%. General formula (I): (In the formula, R ₂ and R ₃ are an alkyl group having 1 to 6 carbon atoms and / or a phenyl group, and R ₁ and R ₄ are represented by the general formula (II): R ₅ is a hydrogen atom or a methyl group, and R ₆ is an alkylene group having 2 to 10 carbon atoms. m is an integer of 0-5. Further, n is an integer of 5 to 50. ) General formula (III): General formula (IV): General formula (V): General formula (VI): General formula (VII): General formula (VII): [In the formula, R ₇ is a trivalent hydrocarbon group having 3 to 10 carbon atoms, and R _{8 is}
Represents an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group or a phenyl group. R ₉ and R ₁₀ represent an alkylene group having 1 to 4 carbon atoms. X and Y are ester-forming functional groups, M
Represents an alkali metal atom, hydrogen or an alkyl group having 1 to 4 carbon atoms. ]